The overall goal of this project is to determine the factors which govern the efficiency of the sarcoplasmic reticulum in the coupling of ATP utilization to the regulation of intracellular Ca ions levels in cardiac muscle. These studies proposed here center initially on a determination of the dynamical structure at the submolecular level of the sarcoplasmic reticulum membrane and its functionally relevant model membrane as determined by X-ray and neutron diffraction. The dynamical structure of the natural and model membrane will be studied "at rest" and during the time-course of Ca ions uptake and Ca ions release. Through such studies and a correlation of systematic structural and dynamical modification of the membranes with their resulting perturbed energy-coupling efficiencies, we hope to gain insight into the molecular mechanism of Ca ions transport and the structural and dynamical factors which govern the degree of energy coupling in this regulatory membrane.